In the manufacture of semiconductors, electrical connections are made between electrical terminals on the semiconductor and corresponding electrical terminals on the substrate for the semiconductor. One method for making these interconnections uses solder or polymeric material that is applied to the terminals. The terminals are aligned and contacted together and the resulting assembly of semiconductor and substrate heated to reflow the solder or polymeric material and solidify the connection. The space between the solder or polymeric connections are filled with a polymeric encapsulant or underfill to reinforce the interconnect and to absorb stress. Two prominent uses for underfill technology are in packages known in the industry as flip-chip, in which a semiconductor chip is attached to a lead frame, and ball grid array, in which a package of one or more chips is attached to a printed wire board.
In some operations the underfill process is designed so that the underfill encapsulant should cure at a higher temperature than that at which the solder or polymeric interconnect material reflows. In the case where the interconnect is lead free, the flow temperature can be as high as 217° C. Thus, the curing temperature of the underfill encapsulant needs to be higher than this temperature. Typical underfill compositions include epoxy, epoxy/phenol, epoxy/anhydride, and cyanate ester systems. These do not always cure at temperatures high enough for the underfill operations using polymeric solder without volatilizing off and, therefore, a need exists for performance materials for high temperature underfill.